Technical Field
This disclosure generally relates to microbiological treatment of fluids containing one or more contaminants, more particularly to microbiological treatment systems and methods using powdered natural lignocellulosic materials (“PNLMs”).
Description of the Related Art
Biological treatment systems are found throughout the municipal, industrial, and commercial water treatment fields. A biological treatment system, maintains conditions favorable for microbial development (e.g., pH, dissolved oxygen, nutrients, and temperature) such that the biological organisms present in the system convert at least a portion of the contaminants or other substances present in the water to biological growth (i.e., increase in biomass) and to one or more preferred byproducts such as water, carbon dioxide, and methane. Traditionally, biological treatment systems treated potable water waste such as sewage collected from residential, institutional, commercial, and industrial establishments. At times, the biological treatment system may receive additional waste from industry and commerce. At other times, the biological treatment system may also receive a quantity of storm water runoff particularly in industrial and commercial settings. Given the disparate nature of the sources generating the wastewater, biological treatment facilities may receive any combination of sewage waste, dirt, debris, oil, and grease.
To accommodate variable wastewater conditions, biological treatment systems generally comprise three stages, often referred to as primary treatment, secondary treatment, and tertiary treatment. Incoming wastewater passes through a number of screens, filters, or sieves to remove large and/or dense debris (e.g., sand, rocks, rags, sticks, plastic bags, and other “trash”). The screened wastewater flows to the primary treatment stage. The primary treatment stage frequently involves the use of quiescent settling ponds or basins to receive the incoming wastewater. The heavier solids present in the wastewater tend to sink in the settling basin and are removed using drags, scrapers, or similar equipment. Lighter materials such as oil and grease and buoyant solids tend to float in the settling basin and are removed using skimmers or similar equipment. In at least some instances, one or more flocculating agents may be introduced to the settling basins to promote the formation of denser, more easily settled solids. In at least some instances, dissolved air may be introduced to the settling basins to promote the formation of more easily skimmed foam or froth containing at least a portion of the oils and greases present in the wastewater. Clarified water, now free of the heavier and lighter solids removed in the settling basin flows from the primary treatment stage to the secondary treatment stage.
Secondary treatment degrades the sewage derived from human waste, food waste, soaps, detergents, animal processing, organic and inorganic fertilizer runoff, and the like. The secondary treatment stage may also include one or more substance-specific microbiological organisms used to degrade contaminants found in the wastewater, for example hydrocarbons that may be present in wastewater generated during hydrocarbon processing operations or street/parking lot runoff. The secondary treatment process typically involves the use of an aerobic biological process in which bacteria and protozoa in an aerator consume biodegradable soluble organic contaminants such as sugars, fats, organic short-chain carbon molecules, and the like and bind other less soluble fractions into a flocculated mass.
Secondary treatment systems can include fixed-film or attached-growth systems in which microbial growth occurs on a surface that is in continuous or intermittent contact with the wastewater. Typical examples include trickling filters, biotowers, and rotating biological contactors. Secondary treatment systems may include activated sludge treatment systems that force an oxygen containing gas through the aerator to promote the growth of biological floc to remove organic materials from the wastewater. Other forms of secondary treatment include aerobic granular sludge, surface-aerated basins, filter beds, constructed wetlands, biological aerated filters, rotating biological contactors, and membrane reactors.
The sludge formed in the secondary treatment system is clarified and settled in a separator such as a clarifier-settler. In some instances, a portion of the sludge may be recycled to the facility influent to consistently maintain a microbial population acclimated to the particular constituents, contaminants, or substances present in the incoming wastewater. At least a portion of the settled sludge may be further processed to remove additional water, for example via one or more centrifugal separators or filters prior to disposal.